1. Field of the Invention
The present invention relates to a method for forming a resist under layer film, a pattern forming method and a composition for a resist under layer film.
2. Discussion of the Background
In the process for producing an element of a highly integrated circuit, miniaturization of the working size using a multilayer resist process is progressing in order to achieve higher integration. In this process, a liquid composition for forming a resist under layer film is first coated onto a substrate and then a liquid photoresist composition is further coated thereon. Next, a mask pattern is transferred onto the photoresist film using a reduced projection exposure system (stepper), followed by development using an appropriate developer to obtain a photoresist pattern. After that, the pattern is transferred onto a resist under layer film by dry-etching. Finally, the resist under layer film pattern is transferred onto a substrate by dry-etching to obtain a substrate with a desired pattern. A multilayer process using one type of resist under layer film is called a bilayer resist process and a multilayer process using two types of resist under layer film is called a trilayer resist process.
A resist under layer film generally functions as an anti-reflection film which absorbs radiation reflected by a substrate. Additionally, a material having a large content of carbon atoms is used for a resist under layer film directly in contact with a substrate and exhibits good etching resistance during processing a substrate and ensures more accurate pattern transfer. A thermoset phenol novolac is a particularly well-known material for such a resist under layer film. Further, a composition containing a polymer possessing an acenaphthylene skeleton is known to have good characteristics as a resist under layer film (disclosed in, for example, Japanese Unexamined Patent Application Publication No. JP-A 2000-143937 and Japanese Unexamined Patent Application Publication No. JP-A 2001-40293).